7 January 2000


Patch spraying techniques are not just for

pesticides – they can also be used to financial

advantage for liquid fertiliser applications

THE main aim when patch spraying technology was being developed was to allow herbicide application rates to be matched to varying levels of weed infestation.

This aim however, was not the priority on the Lincolnshire farm which was the first in the UK to invest in a patch sprayer.

When Paul Steer ordered a sprayer fitted with the Micron patch spraying system for the 292ha (722 acres) he manages for C G R Booth Farms, his main interest was to reduce costs by varying application rates for liquid fertiliser.

Now, after 20 months with the patch sprayer, savings on P and K average £12.10 per hectare, and he has saved a further £8.30/ha by varying the rate for nitrogen.

The P & K savings, plus £1.50/ha off the fungicide bill, are across the farm, but the variable rate nitrogen application has only been tried on four fields so far as Mr Steer extends his use of the new technology.

Varying the fertiliser rates was the obvious starting point. The farm, at Thornton Curtis near Barton upon Humber has a Massey Ferguson combine equipped for yield mapping, and Mr Steer had built up four years of yield data when the sprayer arrived in the spring of 1998.

P and K rates are determined by calculating the amounts actually removed by the crops including, where appropriate, the straw. These rates are increased where soil analysis has identified a low P or K status, with the aim of achieving a gradual build-up of nutrient levels in these areas.

"This may not be the correct way to work out what the rates should be," says Mr Steer, "But I am quite sure it makes a lot more sense than using guesswork and the same amount of P and K right across the field."

A recent land drainage programme was based largely on the farms yield map data, and the yield information also provided the basis for calculating the payback period for the scheme. Yield information is now being used to calculate the variable rate N2 application, which was introduced cautiously in 1998 with plot scale trials, using the combine harvester to check for yield differences.

An extension for last years harvest covered four complete fields, and with yield figures suggesting the crops have not suffered from the change in the nitrogen application, Mr. Steer is planning to vary the rate over the whole farm this year, reducing the rate by up to 30% on areas identified as low yielding.

N2 rates are 90% yield map based, and the other 10% is adjustments based on his own judgement.

As well as fertiliser and fungicide applications, Mr Steer believes there is the potential for savings from varying the application rate for growth regulators. He is also interested in patch spraying with herbicides – the job the equipment was originally developed to deal with.

Logical development

"Patch spraying would be a logical development, but at this stage I dont have the information I would need to prepare the weed maps," he says. "It is possible to record weed information while the crop is being harvested, but that seems to be the wrong stage because some of the weeds are not visible at harvest time. In any case, driving a combine is a big enough job without trying to record weeds at the same time."

Mr Steer has considered mapping with equipment carried on an ATV – but he is concerned about the time it would take, and he is hoping a more suitable method may emerge from the mapping research project at Silsoe.

"They have been doing a lot of work on different methods of weed mapping, and they may come up with something. Weed control is not a major problem here, and variable rate fertiliser application offered more potential for cutting costs," he says.

"But if Silsoe or anyone else comes up with a suitable method of weed mapping I would certainly be interested."

Paul Steer drives the sprayer and also prepares the field maps which control the variable application rate. He says all the equipment is easy to operate and works efficiently.

There is particular praise for the latest updated version of the MF field mapping programme which he describes as "excellent" and easy to use.

The Micron variable rate control package was fitted to a new demount sprayer with a 2500-litre tank and a 28m boom. The sprayer is a standard model from the Gem range – now Case IH – and is mounted on a JCB Fastrac 1135 tractor with an extended chassis.

The results so far of the switch to variable rates are encouraging, says Mr Steer. Total savings this year were £21.90/ha on the four fields where the nitrogen rate was varied, reducing to £13.60 where Mr Steer was still using nitrogen at a flat rate, and he is confident that further savings will be available as he extends the use of the equipment.

Crop yields were significantly higher this year, but this was due to the season, making it difficult to measure the effects of the change of spray technique.

"Where I have been able to make comparisons on different parts of a field, the field figures on the combine have not identified any differences," says Mr Steer. "The only difference is in the costings. I doubt if the financial situation for arable farming will improve very much over the next few years, and variable rate spray application could make a significant contribution to cost reduction."

The Micron variable rate control system is available for new sprayers or for retro-fitting to existing equipment. The cost of the equipment including an interface to an existing GPS linked control system is from £4,500. &#42

The Gem sprayer with the Micron variable rate control system is mounted on a Fastrac 1135 with an extended chassis.

The white box above the sprayer contains the variable rate control system.

Paul Steer is pleased with the cost savings already achieved with the patch sprayer.